Help with DC on volume pot

[Mooly]

It would make for a neater job, that's for sure. Just make sure you have enough space to fit what you want.

 

[mkusan]

Not sure what to suggest on a sticky meter. Again they are fragile, the pivots are jewelled, in fact just like a watch balance wheel and hairspring. Any ordinary oil will be far too thick, probably something like a watch or clock oil would be good. I imagine you would have to take the movement out of the meter case to get at the lower bearing.

Something that might help... rig up a 555 timer as a low frequency oscillator to pulse the meter fully to 100% every second and leave it for a day or so. That might help free up a sticky bearing.

I just wanted to give some feedback to the community.

That the amplifier is indeed repaired was further proven by operating low filter switch while monitoring dc-offset. Operating it before caused rises up to 200mV in dc-offset, now it makes no influence at all.

As for stuck vu-meter, I built 555 timer circuit as you suggested Mooly.
After only 8 hours of needle exercise things very much improved , I started off with slight shaking around 20db.

I was just wondering if after couple of days the needle still doesn't descend fully to the left, is it safe to reverse poles on the meter side so the needle works more to the left? Movie uploaded here:

vu-meter.MOV - YouTube


BTW, I googled "stuck vu-meter" and in my searches I never came across timer 555 circuit as proposed solution for this. DVM on diode test was one of the solutions, but I believe this is way more easier than holding probes in hands for a couple of days. Brilliant idea which is now confirmed in practice as being highly effective.

 

[Mooly]

It won't harm the meter to drive it the other way as long as you don't overdo it. Maybe limit the reverse voltage to around 50% of normal F.S.D. value. It's not that you'll burn the movement out, it's just the mechanical shock of it hitting the end stops repeatedly. So just keep it at sensible limits and it will be fine.

If the bearings are damaged or really dirty then this may not fix it anyway but it's worth trying.

 

[mkusan]

It won't harm the meter to drive it the other way as long as you don't overdo it. Maybe limit the reverse voltage to around 50% of normal F.S.D. value. It's not that you'll burn the movement out, it's just the mechanical shock of it hitting the end stops repeatedly. So just keep it at sensible limits and it will be fine.

If the bearings are damaged or really dirty then this may not fix it anyway but it's worth trying.

Hi Mooly,
F.S.D. I presume is not Fire Service Department?

Thanks
Marko

 

[Mooly]

Full scale deflection

 

[mkusan]

Full scale deflection

That makes more sense

 

[mkusan]

It won't harm the meter to drive it the other way as long as you don't overdo it. Maybe limit the reverse voltage to around 50% of normal F.S.D. value. It's not that you'll burn the movement out, it's just the mechanical shock of it hitting the end stops repeatedly. So just keep it at sensible limits and it will be fine.

If the bearings are damaged or really dirty then this may not fix it anyway but it's worth trying.

Hi Mooly,
It turned out it wasn't necessary to drive meter the other way around.
This morning I was greeted with with needle movement across the entire range (F.S.D)

With great sadness I leave this topic as I have nothing more to fix on Rotel

I would like to thank each and everyone who contributed , since I acquired here what is known as soldering bug, and a headphone amplifier kit is on its way from China I promise I will be back.

 

[Mooly]

Thanks for update... we got there in the end

Good luck with the headphone amp.